Photolithographic image formation in a photosensitive polymer layer followed by plasma-based transfer of the defined photoresist patterns into other materials has been remarkably successful in enabling the production of micro- and nanometer-scale electronic features. This has required a continuous evolution of materials and patterning techniques such as new photolithography systems, appropriate photo-polymer resists, and innovative etching equipment and processes.
For patterned structures, the critical dimension (CD) relates to the width of the patterned structures, e.g. patterned lines. The variation of the line width is expressed by the Line Width Roughness (LWR) value. The variation of the edges of the line with respect to an ideal case is expressed as Line Edge Roughness (LER).
The manufacturing of sub-20 nm technologies has triggered a radical change in photoresist-materials; consequently, this technology has to face many new challenges such as controlling line width and line edge roughness (LWR and LER). Effects of line width roughness and line edge roughness become more important as feature dimensions become smaller, which makes the control of LWR and LER a major scaling concern. This line width roughness, defined as the 3σ critical dimension (CD) variation along a segment of a line, is having a big impact on the transistor performance. In addition, increased LWR also induces higher variance in device performance which can affect circuit stability. Devices fabricated with the 20 nm node technology are for instance required to have a maximum allowable LWR which is smaller than or equal to 2 nm. The current best LWR that can be achieved in photoresist using EUV lithography is about 3 to 4 nm. A substantial improvement in LWR of the patterned structures is required to minimize the impact on device performance.
Directed self-assembly (DSA) of block-copolymers is an emergent alternative approach to nanolithography. Block-copolymers consist of chemically different polymer blocks interconnected by covalent bonds. The chemically different polymer blocks undergo a microphase separation, which is driven by repulsion between the dissimilar polymer chains, such that homogenous domains in a periodic nanostructure are formed after annealing. The type of structure which is formed is for instance controllable by tuning the ratios of the different polymer block lengths. However, the block-copolymer material may feature random orientation and a poor long-range order when not constrained by orientation control techniques. Such techniques, for example grapho-epitaxy or chemical epitaxy, selectively direct the formation of domains in the block-copolymer material. Through subsequent selective removal of one polymer type, a patterned structure of gaps is formed which can be used as a resist layer on the underlying substrate.
In “Defect source analysis of directed self-assembly process (DSA of DSA)”, Paulina Rincon Delgadillo et al., Proc. of SPIE Vol. 8680, 86800L, 2013, the use of a DSA technique for patterning is described, known as the Liu-Nealey flow or “LiNe flow”. The Liu-Nealey flow process combines standard lithography to direct the self assembly of lamellar block-copolymers to fabricate features at a finer pitch than can be achieved with lithography alone.
European Patent Application No. 2717296 and U.S. Pat. No. 8,828,253 relate to methods that provide high selectivity in the removal of a first component of a phase separated DSA layer with respect to a second component, the latter being then used to pattern an underlying layer. Such a highly selective material removal may increase the overall performance of the process with respect to LWR and/or LER of the patterned underlying layer.
Although relatively good performance with respect to LER and LWR can be achieved with DSA, there still exists a need to further reduce LWR and LER, for instance for sub-20 nm technologies.